Conventionally, lighting apparatuses that dim a solid state light-emitting element such as a light-emitting diode according to a dimming signal from a dimmer are known.
As a lighting apparatus of this type, a power supply apparatus has been proposed which cancels a dimming signal for a predetermined period of time immediately after power-on to light a light-emitting diode at a prescribed light intensity and which removes the cancellation after a lapse of the predetermined period of time to light the light-emitting diode at a light intensity instructed by the dimming signal (JP 2009-232625 A1 (hereinafter, referred to as “Document 1”)).
As shown in FIG. 23, the power supply apparatus disclosed in Document 1 includes a full-wave rectifying circuit 62, a ripple current smoothing capacitor 63, a switching transformer 64, a switching transistor 65, a control circuit 66, and a dimmer operating unit 67. The full-wave rectifying circuit 62 generates output that is a full-wave rectification of AC power from an AC power supply 61.
In addition, in the power supply apparatus described above, a rectifying smoothing circuit 70 including a diode 68 and a smoothing capacitor 69 is connected in parallel to a secondary winding 64b of the switching transformer 64. Furthermore, in the power supply apparatus, a plurality of (in the illustrated example, four) series-connected light-emitting diodes 71 to 74 are connected in parallel to the smoothing capacitor 69. Moreover, Document 1 discloses a lighting fixture to which the power supply apparatus described above is applied.
In the power supply apparatus described above, a series circuit which series-connects the plurality of light-emitting diodes 71 to 74 is connected between both ends of the smoothing capacitor 69. Therefore, when power is supplied to the power supply apparatus described above, it is estimated that the smoothing capacitor 69 is to be charged until a voltage across the smoothing capacitor 69 reaches a total voltage of forward voltage (forward direction voltage) of the respective light-emitting diodes 71 to 74. In this case, a charging time required to charge the smoothing capacitor 69 is determined by a magnitude of an average value of a current flowing through the secondary winding 64b of the switching transformer 64.
In addition, with the power supply apparatus described above, since the magnitude of the average value is determined by a duty ratio of a dimming signal from the dimmer operating unit 67, for example, when the respective light-emitting diodes 71 to 74 are dimmed at a dimming level that is a lower limit of dimming of the respective light-emitting diodes 71 to 74, the magnitude of the average value decreases. Therefore, with the power supply apparatus described above, when the respective light-emitting diodes 71 to 74 are dimmed at the dimming level described above, the charging time required to charge the smoothing capacitor 69 may increase and a period of time from an unlighted state to dimming of the respective light-emitting diodes 71 to 74 may become comparatively longer.
Furthermore, with the power supply apparatus described above, there is also a concern that a period of time required until the respective light-emitting diodes 71 to 74 are lighted may be further extended due to the cancellation of the dimming signal for a predetermined period of time immediately after power-on.